1. Field of the Invention
The present invention relates to a semiconductor device, and particularly to a semiconductor device including a thin film resistor, a bleeder resistor circuit using a thin film resistor, and a semiconductor device including the bleeder resistor circuit.
2. Description of the Related Art
Although a number of resistors formed of semiconductor thin films of polysilicon or the like, and a number of bleeder resistor circuits using those resistors have been conventionally used, the known resistor is made of a semiconductor thin film of either one of an N type and a P type.
However, in the conventional thin film resistor, in the case where stress is applied to the thin film resistor, for example, in the case where it is resin packaged, there has been a problem that its resistance value is changed, and in the bleeder resistor circuit, a voltage dividing ratio is often changed after resin packaging.
The present invention has been made to solve the foregoing problem and has an object to provide semiconductor device including a thin film resistor which can keep an initial resistance value even after packaging, a high precision bleeder resistor circuit which can keep an accurate voltage dividing ratio even after packaging, and a high precision semiconductor device using such a bleeder resistor circuit, for example, a voltage detector, a voltage regulator, or the like.
In order to achieve the above object, according to the present invention, a thin film resistor or a thin film resistor of a bleeder resistor circuit using thin film resistors is constituted by a P-type thin film resistor made of a P-type semiconductor thin film and an N-type thin film resistor made of an N-type semiconductor thin film. Further, in the bleeder resistor circuit, a resistance value of one unit is regulated by a resistance value formed by a combination of the P-type thin film resistor and the N-type thin film resistor, so that changes of resistance values in the P-type thin film resistor and the N-type thin film resistor by a piezo effect described below cancel out each other.
The changes of the resistance values by the piezo effect and the influence on the bleeder resistor circuit will be described below.
In the case where stress is applied to the thin film resistor, although the resistance value of the thin film resistor is changed by the so-called piezo effect, the directions of the changes of the resistance values become opposite between the P-type thin film resistor and the N-type thin film resistor. This is also ascertained through experiments by the present inventor. For example, the resistance value of the P-type thin film resistor is decreased, and the resistance value of the N-type thin film resistor is increased (the directions of the changes depend on the direction of the stress).
When an IC is resin packaged, stress is generated so that the resistance value of the thin film resistor is changed by the piezo effect as described above. Although the bleeder resistor circuit is for obtaining an accurate voltage dividing ratio, the resistance values of the respective resistors are changed so that the voltage dividing ratio is also changed.
Since the thin film resistor of the present invention is constituted by the P-type thin film resistor made of the P-type semiconductor thin film and the N-type thin film resistor made of the N-type semiconductor thin film, even in the case where the stress is applied, a change in the resistance value can be prevented. Besides, in the bleeder resistor circuit, since the resistance value of one unit is regulated by the resistance value formed by a combination of the P-type thin film resistor and the N-type thin film resistor, even in the case where stress is applied, the changes in resistance value of the respective resistors cancel each other out, and accurate voltage dividing ratio can be maintained.
Since the thin film resistor of the semiconductor device of the present invention is constituted by the P-type thin film resistor made of the P-type semiconductor thin film and the N-type thin film resistor made of the N-type semiconductor thin film, even in the case where stress is applied by resin packaging or the like, the changes of the resistance values of the respective resistors cancel out each other and the initial resistance value can be kept. Besides, in the bleeder resistor circuit, since the resistance value of one unit is regulated by a resistance value formed by a combination of the P-type thin film resistor and the N-type thin film resistor, an accurate voltage dividing ratio can be kept. By using such a bleeder resistor circuit, a high precision semiconductor device, for example, a voltage detector, a voltage regulator, or the like can be obtained.